Adjustable electrical components formed from arrays of differential circuit elements

Title: Adjustable electrical components formed from arrays of differential circuit elements.Abstract: Adjustable circuit components may be formed from arrays of differential circuit elements such as differential capacitors and differential current sources. The differential circuit elements may each have a control input. The differential circuit elements in each array of differential circuit elements may be connected in parallel between first and second terminals. A thermometer code control signal may be provided to the control inputs to adjust the capacitance, current, or other parameter associated with the adjustable circuit component. Adjustable circuit components may also be formed from an array of capacitors or other circuit elements having successively increasing strengths. ...

BACKGROUND

This invention relates to adjustable electrical components, and more particularly, to adjustable electrical components formed from arrays of differential circuit elements.

It is often desirable to produce integrated circuits with adjustable circuit components. For example, it may be desirable to product a digitally controlled variable capacitor or a digitally controlled current source. Components such as these may be used to adjust the operation of complex analog and digital circuits.

Accurate operation of an adjustable circuit element may be essential to proper operation of a more complex circuit. For example, it may be critical that an adjustable capacitor or current source exhibit a high degree of linearity with respect to its control input. Adjustable circuit elements that are inaccurate may cause the circuitry within which they are embedded to fail.

It would therefore be desirable to be able to provide improved adjustable circuit elements.

SUMMARY

In accordance with the present invention, adjustable circuit components such as adjustable capacitors and adjustable current sources may be provided. The adjustable circuit components may be formed from arrays of differential circuit elements connected in parallel. The differential circuit elements may be circuit elements such as differential capacitors and differential current sources.

Each differential circuit element may include first and second devices such as first and second capacitors or first and second current sources. The capacitances of the first and second capacitors may be different and the magnitudes of the currents produced by the first and second current sources may be different. Within a given adjustable circuit component, the first devices may have a common value such as a common capacitance or a common current source strength and the second devices may have a common value such as a common capacitance or a common current source strength.

First and second switches in each of the differential circuit elements may be used to selectively switch either the first device or the second device in that element into use. The differential circuit elements may each have a control input at which a control signal is received. An inverter in each differential circuit element may invert the control signal. The control signal may control the first switch and the inverted version of the control signal may control the second switch.

The differential circuit elements in each array of differential circuit elements may be connected in parallel between first and second terminals. A thermometer code control signal may be provided to the control inputs to adjust the capacitance, current, or other parameter associated with the adjustable circuit component.

The adjustable circuit elements may be used to adjust the operation of circuitry such as ring oscillator circuitry and phase-locked loop circuitry.

Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an illustrative digitally controlled oscillator based on a loop of single-ended inverters and digitally controlled capacitors in accordance with an embodiment of the present invention.

FIG. 2 is a diagram of an illustrative digitally controlled oscillator based on a loop of differential inverters and digitally controlled capacitors in accordance with an embodiment of the present invention.

FIG. 3 is a diagram of an illustrative digital phase-locked loop that may use a digitally controlled oscillator with digitally controlled capacitors in accordance with an embodiment of the present invention.

FIG. 4 is a diagram of an n-channel metal-oxide-semiconductor transistor in accordance with an embodiment of the present invention.

FIG. 5 is a diagram of a capacitor formed from an n-channel metal-oxide-semiconductor transistor in accordance with an embodiment of the present invention.

FIG. 6 is a diagram of a capacitor formed from a p-channel metal-oxide-semiconductor transistor in accordance with an embodiment of the present invention.

FIG. 7 is a diagram of a capacitor formed from an n-channel or p-channel metal-oxide-semiconductor transistor in accordance with an embodiment of the present invention.

FIG. 8 is a cross-sectional side view of an illustrative integrated circuit capacitor formed from an n-channel metal-oxide-semiconductor transistor in accordance with an embodiment of the present invention.

FIG. 9 is a diagram of an adjustable capacitor based on an array of individually selectable capacitors of increasing value in accordance with an embodiment of the present invention.

FIG. 10 is a table of illustrative capacitor values that may be used for the capacitors in a capacitor array of the type shown in FIG. 9 in accordance with an embodiment of the present invention.

FIG. 11 is a table showing an illustrative one-hot digital control word for use in controlling a digital capacitor formed from an array of capacitors of the type shown in FIG. 9 in accordance with an embodiment of the present invention.

FIG. 12 is a table showing another illustrative one-hot digital control word for use in controlling a digital capacitor formed from an array of capacitors of the type shown in FIG. 9 in accordance with an embodiment of the present invention.

FIG. 13 is a diagram of an illustrative delta capacitor in accordance with an embodiment of the present invention.

FIG. 14 is a diagram of an illustrative adjustable capacitor formed from an array of delta capacitors of the type shown in FIG. 13 in accordance with an embodiment of the present invention.

FIG. 15 is a table of illustrative capacitor values that may be used for the capacitors in an array of delta capacitors in accordance with an embodiment of the present invention.

FIG. 16 is a table showing an illustrative thermometer code digital control word for use in controlling a digital capacitor formed from an array of delta capacitors in accordance with an embodiment of the present invention.

FIG. 17 is a table showing another illustrative thermometer code digital control word for use in controlling a digital capacitor formed from an array of delta capacitors in accordance with an embodiment of the present invention.

FIG. 18 is a circuit diagram of an illustrative differential current source that may be used in an array of differential current sources in accordance with an embodiment of the present invention.

FIG. 19 is a circuit diagram of an illustrative adjustable current source formed from an array of differential current sources of the type shown in FIG. 18 in accordance with an embodiment of the present invention.

FIG. 20 is a diagram showing the sizes of illustrative circuit structures in an array of circuit elements controlled by a control signal encoded using a one-hot encoding scheme in accordance with an embodiment of the present invention.

FIG. 21 is a diagram showing the sizes of illustrative circuit structures in an array of circuit elements controlled by a control signal encoded using a thermometer code encoding scheme in accordance with an embodiment of the present invention.

FIG. 22 is a diagram of an illustrative varactor that may be used in adjustable capacitors in accordance with embodiments of the present invention.

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20100107|20100001784|adjustable electrical components formed from arrays of differential circuit elements|Adjustable circuit components may be formed from arrays of differential circuit elements such as differential capacitors and differential current sources. The differential circuit elements may each have a control input. The differential circuit elements in each array of differential circuit elements may be connected in parallel between first and second |